It is well established that ceramides have a vital role in the production and maintenance of the water permeability barrier of the skin. Ceramides, or substances closely related to them, have been widely disclosed as components of skin care compositions.
In particular EP 0 097 059 (Unilever) discloses the vital role played by .omega.-linoleoyl ceramides in the water barrier of the skin and describes the application for skin care of such .omega.-linoleoyl ceramides.
It is known in the art that skin ceramides (including .omega.-hydroxy fatty acid containing ceramides) may be extracted from mammalian stratum corneum cells.
It has been proposed for example in U.S. Pat. No. 3,660,566 (Lever Brothers Company), to extract animal stratum corneum from epidermis and then separate the stratum corneum into a lipid-rich fraction and a cellular fraction, and then to employ the lipid-rich fraction in cosmetic compositions.
It is also proposed in GB 2 178 312 (Kao Corporation) to extract lipids from horny cells of mammals such as the pig, and then to employ the lipid so extracted in cosmetic compositions which are useful for treating dry skin conditions in man.
However, to extract .omega.-hydroxy fatty acid containing ceramides in high enough levels for incorporation into skin care products causes problems. Furthermore it is undesirable for the source of the cosmetic ingredient to be from animals.
Synthetic Pseudo-ceramides have also been widely disclosed in the literature, for example by Kao Corporation in EP 0 227 994 which discloses synthetic analogues of ceramides which have some similar properties to natural ceramides but which are relatively cheaper to produce. However, the degree of skin benefit attributable to such analogues is limited to the extent that they do not fully mimic the natural ceramides of the skin.
It is therefore desirable to be able to synthesise naturally-occurring .omega.-hydroxy fatty acid containing ceramides using a synthesis route, which is not too expensive, to allow the possibility of the synthesised ceramides being incorporated at functional levels into cosmetic compositions.